Lt. Col. Gary Tingle, the jail division commander, said investigators are not yet sure how long the woman spent in the cell. She has not alleged any wrongdoing on the part of the other inmates.

"As to what caused it, that is still being investigated," Tingle said. "We haven't come to a conclusion at this time."

It's the second time in the last year that a Marion County Jail guard has inadvertently locked a male inmate and a female inmate in the same cell. After an incident last summer, in which the woman claimed the male inmate sexually assaulted her, Sheriff John Layton reprimanded the three deputies working the area and ordered them to undergo remedial training.

He implemented new cellblock policies, including a requirement that labeled and color-coded signage be displayed on all blocks.

Although the course of events in the latest incident are unclear, some details have emerged.

The mix-up happened sometime between 8 and 8:30 a.m. Tuesday, when the 28-year-old inmate was supposed to have been escorted to a female cellblock after her trip to the jail's medical office.

Instead, someone took her to a dormitory-style cellblock for men. Once inside, the woman realized she was in the wrong place and called her mother to complain, she later told investigators.

Jail officers realized the error, Tingle said, after they received a call from the woman's attorney.

But how did a female inmate end up with a group of men in the first place?

"It's a complicated issue," Tingle said. "The facility is antiquated. It's old. We don't have enough space for the number of inmates that we currently house, and so we're constantly changing our cellblocks in order to accommodate the number of beds that we have."

A statement from Layton's office chalked the incident up to the same issue: "chronic jail overcrowding."

At the time of the incident, Tingle said, the jail was holding 936 inmates, 264 of them female.

All of the jail's 71 cellblocks are designated for a specific purpose â?? men in the general population, women in the general population, or men with mental health issues, as examples.

Some of those blocks, however, are switched to a different purpose depending on the jail's need. So a cellblock that is one day being used to house men can the next day be switched and used to house women, Tingle said.

On average, Tingle said a cellblock can change functions about six times per week and sometimes as many as two or three times a day.

Tingle said officials keep note of each cell's designation using a spreadsheet. Before last summer's incident, the block classifications were kept in a main control area. But Tingle said that since then jail officials have implemented more safeguards, such as displaying signage outside each cellblock.

In this case, Tingle said that signage was properly displayed. But it's unclear why that wasn't noticed by the official who took the woman to the wrong cell.

"We're trying to figure out why that was ignored or missed," Tingle said.

Once the woman was inside the block, Tingle said the official might not have realized the mistake. Inmates need to pass through two sets of doors to reach the cellblock, which separates them from the officers. The process can leave other inmates already inside the block out of an official's sight.

"It helps from a safety standpoint," Tingle said. "If inmates wanted to do harm to an officer, he's not opening the door and going directly into a cellblock with them. We have that extra layer between them and us."

During the incident last July, a jail guard locked a male inmate in a cell that was already holding a female inmate. The two inmates were left alone together for as long as five minutes after the male inmate sent the guard on an errand within the jail.

The woman claimed the man sexually assaulted her, but charges were never filed. When outside investigators were brought in to investigate her claim, the woman refused to cooperate and a rape test proved inconclusive.

Contributing: Kristine Guerra and Cathy Knapp of The Indianapolis Star.